1. Field of the Invention
The present invention relates to an in-plane liquid crystal display (LCD) apparatus.
2. Description of the Related Art
In an in-plane LCD apparatus, liquid crystal is driven by an electric field generated horizontally with respect to substrates.
A first prior art in-plane type LCD apparatus includes a comb-shaped source electrode and a comb-shaped common electrode which are interleaved with each other, thus generating a horizontal electric field therebetween. As a result, liquid crystal molecules are rotated in a certain direction by the horizontal electric field (see U.S. Pat. No. 3,807,831 & JP-A-56-91277). This will be explained later in detail.
In the first prior art LCD however, electric fields generated around the tops and bottoms of the comb-shaped portions of the source electrode and the common electrode are radial. As a result, a torque is applied to some of the liquid crystal molecules in an opposite direction. Therefore, some of the liquid crystal molecules are rotated in an opposite direction, which creates extraordinary domains (dark domains). Also, in this case, since a discrimation or a boundary face is created between the extraordinary domains (dark domains) and the ordinary domains (light domains), such a boundary face cannot be controlled, and therefore, is unstable.
In a second prior art in-plane type LCD apparatus (see JP-A-7-36058), a part of the source electrode and a part of the common electrode are enlarged to suppress the above-mentioned extraordinary domains. This will also be explained later in detail. However, the inventors have found that the second prior art LCD apparatus has never showen a reduction of the extraordinary domains.
In a third prior art in-plane type LCD apparatus (see JP-A-7-36058), a source electrode and a common electrode are both of a ladder type. Also, the source electrode is isolated from the common electrode by an insulating layer. The source electrode is partly superposed onto the common electrode, to increase the capacitance therebetween. As a result, the numerical apperture can be increased, and the voltage retention characteristics can be improved, In addition, short-circuit and disconnection of the source electrode and the common electrode can be avoided, which increases the manufacturing yield. This will also be explained later in detail.
Even in the third prior art LCD apparatus, however, electric fields generated around the edged portions of the source electrode and the common electrode are radial. As a result, some of the liquid crystal molecules are rotated in an opposite direction, which creates extraordinary domains (dark domains).
Also, a fourth prior art in-plane type LCD apparatus improves visible angle characteristics as compared with TN-type LCD apparatuses (see JP-A-5-505247), corresponding to WO 91/10936). However, this fourth prior art in-plane type LCD apparatus has comb-type electrodes to create the above-mentioned extraordinary domains, which degrades the picture quality.